This invention relates to an video recording/reproducing apparatus for recording video signals on recording media or for reproducing video signals from the recording media, and more particularly to a circuit for restoring horizontal and vertical synchronizing signals included in video signals.
Generally, in order to display video information accurately on an video display device, e.g., a cathode ray tube, a composite video signal comprises a horizontal synchronizing signal in which during a horizontal scanning period, display information is specified by an election beam from left to right and during a horizontal blanking period, the movement of the election beam is specified from right to left, a vertical synchronizing signal in which during a vertical scanning period, display information is specified by the election beam from top to bottom and during a vertical blanking period, the movement of the electron beam is specified from bottom to top, and video information arranged in the scanning period of the aforementioned horizontal and vertical synchronizing signals. The composite video signal including the above horizontal and vertical synchronizing signals and video information, are affected by noise while being transmitted through transmission media such as the air, magnetic tape cassettes, compact disk videos, and accordingly the scanning period and blanking period of the synchronizing signal are altered. As a result, the blanking period encroaches upon the video information period within the scanning period and the image displayed on the video display device oscillates from left to right or from top to bottom. Moreover, a conventional video recording/reproducing apparatus records video signals received by a built-in tuner or external video signals received from the outside on the recording media without correcting the synchronizing signals included in the video signals during recording, and outputs video signals reproduced from the recording media to a display device mounted externally without correcting the synchronizing signals included in the video signal during reproducing. Therefore, the video signal recorded or reproduced using a conventional video recording/reproducing apparatus has a scattered synchronizing signal, and thus, the picture displayed on the video display device has the problem of being severely shaken from left to right or from top to bottom.
Accordingly, it is an object of this invention to provide a synchronizing signal restoration circuit for correcting the synchronizing periods of synchronizing signals included in video signals to prevent the shaking of the video displayed on a video display device in a video recording/reproducing apparatus.
To accomplish the above object, there is provided a synchronizing signal restoration circuit for restoring scattered synchronizing signals included in video signals adapted to a video recording/reproducing apparatus, and includes:
an input terminal for receiving video signals to be reproduced or recorded;
a synchronizing signal separator for separating synchronizing signals from video signals supplied through the input terminal;
a standard clock pulse generator for generating a standard clock pulse train having a period of time much shorter than that of the separated synchronizing signal;
an even/odd field detector for receiving the separated synchronizing signals and the standard clock pulse train and detecting whether the video signal input to the input terminal is of an even or an odd field;
a synchronizing pattern generator for responding to the detected results of the even/odd field detector to generate recognizing pattern data corresponding to the respective fields using the standard clock pulse train;
a composite synchronizing signal generator for generating composite synchronizing signals by differently dividing the frequency of the standard clock pulse train according to the value of the synchronizing pattern data; and
an adder for adding the composite synchronizing signal generated in the composite synchronizing signal generator to the video signal input to the input terminal.